Google, which runs the Android mobile phone operating system, wrote in a blog post that a billion apps were now being downloaded every month, and the rate is accelerating.

But it was a slow start. Google claims that the first 1 billion app installs from Android Market took nearly 20 months, and the second billion took five months. But it only took two months to clock up 3 billion, with more half a million new Android phones are

now activated globally every day.

The figures reflect a renewed priority by Google on its app sales and downloads, with the online giant having launched movie rentals and redesigned the Android Market to go head to head with Apple’s App Store, which has amassed more than 18 billion downloads.

However, Google has benefitted from huge numbers of manufacturers adopting its open-source Android operating system.

To celebrate the milestone, Google will make a number of apps available for 10p for 10 days.

The company said “Starting today for the next 10 days, we’ll have a new set of awesome apps available each day for only 10 pence each. Today, we are starting with Asphalt 6 HD, Endomondo Sports Tracker Pro, Fieldrunners HD, Great Little War Game,

Minecraft, Paper Camera, Sketchbook Mobile, Soundhound Infinity and Swiftkey X.”